The work aims to study frication property and wear mechanism of Cr7C3 coating or GCr15 substrate being rubbed with 9310 alloy steel for sprag overrunning clutch. Cr7C3 coating sample was prepared on GCr15 substrate by adopting chemical vapor deposition technology. The thickness and phase composition of Cr7C3 coating and microhardness of both samples (with and without Cr7C3 coating) were analyzed by scanning electron microscope (SEM) (with EDS analysis)，X-ray diffractometer (XRD) and nano-indenter. Friction and wear properties of Cr7C3 coating and GCr15 substrate were investigated with ball-on-disk SRV-4 high temperature tribotester. Wear scar conditions of the materials were characterized systematically with 3D white light interferometer surface profiler and SEM. It was calculated that the thickness of Cr7C3 coating was about 4~6 μm. And it was mainly composed of phase Cr7C3 and phase (Cr,Fe)7C3. Average surface microhardness of the Cr7C3 coating was 22.709 GPa, nearly twice that of GCr15 substrate (11.198 GPa). Under experimental parameters, frication coefficient of the Cr7C3 coating ranged between 0.18~0.24 while that of GCr15 substrate ranged between 0.15~0.20. Wear rate of GCr15 was about 4~6 times that of Cr7C3 coating at the sliding speed of 60 mm/s and normal load of 20~60 N, but 7~11 times that of Cr7C3 coating at the sliding speed of 100 mm/s. The wear mechanism of GCr15 substrate was typical furrow wear, and that of Cr7C3 coating was mainly furrow wear and fatigue wear at the sliding speed of 100 mm/s and normal load of 60 N. Cr7C3 coating has high microhardness and excellent wear resistance, which can contribute to better wear resistance of the substrate and higher usability of sprag overrunning clutch.